A flash crash is a sudden, very sharp drop in the price of a security, index, currency or cryptocurrency that happens within seconds or minutes and is usually followed by a quick recovery. Prices may fall far below any level that news or fundamentals would justify, then bounce back almost as fast. The term became widely used after a crash in US stock markets on 6 May 2010, and it now covers similar events in futures, bonds, foreign exchange and crypto markets.
Flash crashes are linked to modern electronic markets, where automated trading, fragmented order books and stop orders can turn a single large trade into a chain reaction. They differ from a conventional crash or a bear market, which reflect a lasting change in investor views. A flash crash is mainly a failure of market liquidity: for a short time, buyers step away and prices fall through empty space.
Flash crash in plain terms
Picture a busy auction room where, for a few seconds, almost every buyer steps out for a coffee at the same moment. A seller who insists on selling right away gets only whatever the last person left will pay, which may be a fraction of the real value. When the buyers return, prices go back to normal.
In electronic markets, the "buyers stepping out" are often computer programs that stop trading when conditions look strange. A large sell order, or a wave of automatic stop orders, hits a market with very few bids, and the price plunges. The fall is real while it lasts, and people whose orders fill at the bottom can lose a lot of money.
Common causes
- Large market orders. A big market order placed without price limits consumes every bid in the order book until it is filled, at ever lower prices.
- Stop-loss cascades. Falling prices trigger stop-loss orders, which become new sell orders that push prices lower and trigger further stops.
- Liquidity withdrawal. Automated market makers and high-frequency traders may cancel their quotes when volatility spikes, removing the buyers who normally absorb selling.
- Leverage and liquidations. In margin and futures markets, falling prices force the closure of leveraged positions, creating cascading liquidations.
- Errors and manipulation. "Fat-finger" mistakes, faulty algorithms and deliberate tactics such as spoofing have all played a part in individual events.
Notable flash crashes
On 6 May 2010, US share prices fell steeply in the afternoon, with the Dow Jones Industrial Average dropping close to 1,000 points intraday before recovering most of the loss within about half an hour. Some shares briefly traded at a penny and others at absurdly high prices. A joint report by US regulators later pointed to a large automated sell programme in stock index futures meeting already stressed markets. Years afterwards, a London-based trader was prosecuted in the United States for spoofing in the same futures market, and his conduct was said to have contributed to the conditions that day.
Currency markets have had similar episodes. The British pound dropped by roughly 6% against the dollar within minutes in thin Asian trading on 7 October 2016 before partly recovering. In crypto, the price of ether on one US exchange briefly fell from around $300 to about 10 cents in June 2017 after a multimillion-dollar sell order set off margin liquidations and stop orders; the exchange later honoured the trades. Smaller crypto flash crashes on single venues are common because liquidity is spread across many exchanges.
Safeguards and regulation
After 2010, US regulators introduced a "limit up–limit down" mechanism that pauses trading in an individual share when it moves outside a set band, and revised market-wide circuit breakers that halt trading after large index falls. Exchanges can also cancel trades executed at clearly erroneous prices. Many futures and options exchanges use similar price bands and short trading pauses, and some currency platforms widen spreads or pause quoting in extreme conditions.
Crypto markets are less uniform. Most trade around the clock without market-wide halts, though individual exchanges may use price bands, mark prices for liquidations and insurance funds to absorb losses. Traders can reduce their own exposure by using a limit order rather than a market order, by avoiding excessive leverage and by placing stops with care.
Debate
Flash crashes have fed debate about whether high-speed electronic trading makes markets more fragile. Supporters say automated traders narrow spreads and supply liquidity on normal days; critics say that liquidity can disappear exactly when it is needed. Regulators have generally responded with targeted tools, such as circuit breakers and anti-market manipulation enforcement, rather than restrictions on automated trading itself.